The last FAQ for this was lost. I'll touch up this FAQ when i get some free time but for now in short:

There are two times when you may get this. The first is if you can see who uploaded the file and it's stats but when you click download to PC it says error. It means you have run out of download credits. Your download credits are reset at the end of each day, so please wait 24 hours and you will be able to download files again.

If you get Error. when trying to view the download page and cannot see the stats etc. It means it was rejected by a moderator and thus you won't be able to download the file.

When people upload they are added to the gallery. They are also validated. On validation, or sometimes after validation, if the mod removes the file it wont be removed from the gallery pages until the gallery cache system is refreshed. Therefore, broken links will appear between rejection and the gallery refresh time :).

So unfortunately you will not be able to download those files as they were rejected, most likely for copyright but maybe for duplication, so a search may come in useful :)